Stool Culture | Definition and Patient Education

Stool Culture Overview

Stool
cultures are important tools for understanding and treating intestinal illness.
There are many reasons why you may be experiencing uncomfortable intestinal
symptoms. A stool culture examines stool (or fecal) samples for organisms that
may be causing disease.

A stool
culture is the process of growing or “culturing” organisms living in feces to
see if any of them cause disease. A fecal sample is smeared into dishes with
various gels that encourage bacterial growth.

If growth
is seen, the bacteria are examined under a microscope. Samples may be stained
with special dyes to identify the type of bacteria. The organism may also be
exposed to potential drugs that could kill it, to help determine what treatment
may be effective.

Disease-causing
bacteria that are looked for in a basic stool culture include:

Campylobacter
species

Salmonella species

Shigella
species

If you have
recently travelled outside of the U.S. or have other risk factors, other tests
may be added to search for:

Escherichia coli (E. coli) 0157:H7 (Shiga toxins)

Vibrio species

Yersinia entercolitica

Pleisomonas

Aeromonas

Other tests
may be performed at the same time. These may include a test for Clostridium difficile (C. difficile) toxin and an ova and
parasite exam to look for parasites.

Why Is a Stool Culture Performed?

Infections
of the gastrointestinal tract can lead to uncomfortable, potentially dangerous
symptoms. These symptoms may have a variety of causes, however. Testing the stool
for harmful bacteria allows doctors to help pinpoint what may be causing
symptoms. These symptoms can include:

severe, possibly bloody, diarrhea
that lasts for several days

fever

nausea and vomiting

abdominal pain and cramping

A stool culture
can confirm the presence of harmful bacteria. It may also show what treatments
may work to kill an invasive organism. If no dangerous bacteria are present in
the stool culture but symptoms still exist, other explanations like irritable
bowel syndrome, a parasitic infection, or other diagnosis can be explored.

How Is a Stool Culture Performed?

A stool sample is necessary
to perform a stool culture. For most patients, a stool can be collected and
placed into a sample container. You may be given a sample container. This is usually
a clean, dry, wide-mouth container with an airtight lid. You may have to
provide your own sample container. Some labs even include a special kind of
toilet paper that can be used to collect the sample.

A bedpan can be used to
collect a sample. Another simple method to collect a stool sample may be to
loosely place plastic wrap over the toilet seat before defecating. You can then
use the plastic wrap to transfer the sample into the collection container. Try
to avoid mixing urine or regular toilet paper into the sample.

The process can be more
difficult with infants in diapers, or for people with active diarrhea. In some
cases, a cotton swab may be used in the rectum to collect a sample. Plastic
wrap placed in a diaper for an infant may also work. However, it can be
difficult to keep urine away from the stool sample.

The sample must be turned
into a laboratory as soon as possible after it is collected. At the lab, smears
of the stool sample are placed on special plates with a gel called a growth
media. This can help the growth of bacteria that can then be identified through
dye staining, microscope analysis, and other testing.

Beyond Stool Culture: A Healthy Gut

A normal,
healthy person will have a variety of bacteria and other organisms that live
inside their intestines and actually help maintain their health. We know disease-causing
organisms can start to inhabit your intestines and kill off their “good”
cousins.

Broad-spectrum
antibiotics kill off all the bacteria in your intestines. This includes both disease-causing
bacteria as well as the normal flora, i.e. the “good” bacteria. Sometimes, the
normal flora (sometimes called the microbiome) do not reestablish themselves
after the antibiotics destroy them.

Potentially
harmful bacteria that are antibiotic-resistant can survive and take over the
gastrointestinal tract, causing uncomfortable symptoms. C. difficile is one of these harmful bacteria. Infections with C. difficile can be very difficult to
treat. They can also cause pseudomembranous colitis.

A new and
exciting treatment for C. difficile is
fecal bacteriotherapy or a stool substitute transplant. A stool sample from a
donor is implanted into the patient via a colonoscopy. Another procedure
involves a purified bacterial culture implanted in the same way. The healthy
bacteria can colonize the unhealthy gut and help return normal function to
someone with persistent C. difficile
infection.

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